1. Field of the Invention
The invention relates to a method of converting a first pattern consisting of a first matrix of binary pixels into a second, pattern having a lower resolution than the first pattern, in the form of a second matrix having fewer binary pixels than the first matrix, wherein the first matrix is subdivided into adjacent fields and a pixel number representing the number of pixels of one binary value in each field is determined, whereupon each pixel number is compared to a threshold value, as well as an arrangement for implementing the method.
2. Description of the Prior Art
Such a method is known from U.S. Pat. No. 3,676,982, the first pattern being formed by a pseudo-halftone picture, and the second pattern being a reduced version thereof. In this Patent the fields into which the first matrix has been subdivided are quadratic and the pixel number representing the number of pixels having the binary value "1" in each field is determined, and this counted value is compared to a fixed threshold value which is equal to half the pixels of each field. The results of this comparison provide the reduced picture in which each pixel corresponds with a field of the first matrix. However, it may easily happen that the reduced picture is totally useless as a result of the comparison to a fixed threshold value. The fact is, if a number of adjacent fields are to reproduce a pseudo grey-tone which is slightly darker than the average value, more than half the pixels in each field have the binary value "1", and in the reduced picture a black dot will appear for each of them. A plurality of such adjacent fields having a nearly mean grey tone will thus appear in the reduced picture as a completely black zone. The same holds if a plurality of adjacent fields represents a grey tone which slightly exceeds the mean value and turns out white in the reduced picture.